Project Summary Locomotion and other actions in the world depend on perceptual information about the spatial layout of the environment. Interpreting 2-dimensional representations such as maps or radiographs also depends on the perception of spatial information. Early cortical areas in the visual system are exquisitely tuned for coding orientation, and the early cortical representation of visual space is coded in log-polar coordinates suited for the control of eye-movements by a sensory system that has the dual purposes of picking up some information from a large portion of space but gathering high-precision information suitable for face recognition and reading, for example, but also for manual prehension (grasping things), at the center of gaze. Nonetheless, the visual system must impose reference frames in order to interpret orientation information, and we have found in tilted observers that these reference frames seem often to be tied to external references such as gravity rather than to retino-cortical or bodily reference frames. In our work to date, we have shown that there are substantial systematic biases in the coding of spatial orientation, and that these biases are cross-modal, appearing both in the visual and haptic experiences of surface orientation. These representational biases seem be cognitive adaptations that maintain coding precision. In the case of surface orientation in 3D space, our spatial/perceptual representations exaggerate departures from horizontal with something that resembles the first quarter cycle of a sine function, which may be a way of explicitly representing the gravitational component of 3D surface orientation. In the case of line orientation in 2D space, our spatial/perceptual representations again exaggerate departures from the horizontal, though the exaggeration is less pronounced than in the 3D case as one gets farther from horizontal. In the prior grant period we have shown that the 2D bias function is tied to the gravitational reference frame rather than the retinal reference frame. That is, even when looking through a circular reduction tube (to eliminate external visual orientating information) tilted observers perceive line orientation primarily relative to the gravitational reference frame rather than relative to their bodily reference frame. The present work extends this prior work in two ways. First, using more complex orientation stimuli, we will tilt observers to determine whether memory biases for orientation (which show a different pattern) are also yoked to the gravitational reference frame, or whether there is a residual retinotopic bias based on the early cortical overrepresentation of vertical and horizontal. Second we will use multiple methods to examine whether angular biases in the yaw dimension (both for perceived surface orientation and proprioceptive perception of direction) differ from those in the pitch dimension, as preliminary data suggests, and, if so, whether these differences are locked to bodily, visual (ground plane defined), or gravitationally-defined specifications of pitch and yaw axes.